As an example of typical known wireless power transmission systems, there is a power transmission system of a magnetic field coupling type which transmits power from the primary coil of a power transmitting device to the secondary coil of a power receiving device by using a magnetic field. When transmitting power by magnetic field coupling in this system, the magnitude of the magnetic flux passing through each coil greatly affects the electromotive force, and therefore high accuracy is required for the relative positions of the primary coil and secondary coil. Moreover, use of coils makes it difficult to achieve a reduction in device size.
A wireless power transmission system of an electric field coupling type as disclosed in Patent Document 1 is also known. In this system, power is transmitted from the coupling electrode of a power transmitting device to the coupling electrode of a power receiving device via an electric field. With this method, the accuracy required for the relative positions of the coupling electrodes is relatively low, and also the coupling electrodes can be reduced in size and thickness.
FIG. 1 illustrates the basic configuration of the power transmission system disclosed in Patent Document 1. This power transmission system includes a power transmitting device and a power receiving device. The power transmitting device includes a high-frequency high-voltage generating circuit 1, a passive electrode 2, and an active electrode 3. The power receiving device includes a high-frequency high-voltage load circuit 5, a passive electrode 7, and an active electrode 6. When the active electrode 3 of the power transmitting device and the active electrode 6 of the power receiving device are brought into close proximity to each other with an air gap 4 therebetween, these two electrodes are electric-field coupled to each other, forming a strong electric field between the electrodes, thereby enabling power transmission with high transmission efficiency.    Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-531009
As an example of this power receiving device, there are electronic equipment or the like such as a cellular phone or a personal digital assistant (PDA). In recent years, a capacitive input section (touch panel) that offers good operability is increasingly used for the electronic equipment or the like. In this case, there may be situations where the power receiving device is placed on the power transmitting device, and the touch panel is operated while charging the power receiving device. At this time, as described above, the electric field formed between the active electrodes of the power transmitting device and power receiving device may cause fluctuations in potential, resulting in malfunction of the touch panel.